In current wireless networks, there are both operators of access networks and those of service networks, and an access network can be shared by a plurality of service networks and a geographical district can also be provided with services by a plurality of operators of access networks. In such a complex operating mode, functions for discovering and selecting a network become more and more important.
In current wireless communication networks, schemes for implementing network discovery and selection have their own characteristics, but in all these schemes, it is firstly required to acquire an identifier of a network, and then a terminal performs subsequent processing according to information stored in it.
Taking a WiMAX system as an example, in its newly released version of NWG1.1.0, a procedure and method for a WiMAX terminal to discover and select a network are described. Wherein, a procedure for discovering and selecting a network in the case that a terminal stores the configuration information generated when performing a relevant subscription is described. In this case, the base station can optimize the process of accessing the network, including discovering and selecting the network, by using the stored configuration information generated when subscribing. From this version, it can be seen that the current procedure of network discovery and selection as well as accessing based on “information on the last connection” or “configuration information generated when subscribing” comprises the following procedure sequences:
In the case based on “information on the last connection”, a terminal performs a procedure of judging validity of the last download channel descriptor (DCD) count value prior to a procedure of judging validity of a network access provider ID (NAP ID) and a base station ID (BS ID). And if it judges that the DCD count value is invalid, the terminal continues to acquire messages such as a DCD message.
In the case based on “configuration information generated when subscribing”, a terminal directly acquires messages such as a DCD message and then performs a procedure of judging validity of a NAP ID.
According to the IEEE802.16e-2005 protocol, a downlink mapping (DL-MAP) message includes a “DCD count value” and a “BS ID (including a NAP ID)”, and a DCD message (a message sent by a BS periodically, defining characteristics of a downlink physical channel) includes a “configuration change count” and a “network service provider ID (NSP ID) change count value”.
According to the IEEE802.16e-2005 protocol, in downlink synchronization, a terminal always receives a DL-MAP message first to obtain a “DCD count value” and a “BS ID (including NAP ID)”, and then receives control messages such as a DCD message.
Therefore, it can be seen from the above analysis that according to the procedure in current protocols, although the terminal decodes a DL-MAP message first to obtain a “BS ID”, a “NAP ID” and a “DCD count value”, it does not judge validity of the “NAP ID” and “BS ID”, leading to a result that even if the “NAP ID” or “BS ID” decoded from the DL-MAP is invalid, the terminal will still perform a subsequent procedure of obtaining messages such as a DCD message, thus increasing the time taken for a terminal to discover and select a network, and hence affecting the speed of network accessing of the terminal.